Drying process and apparatus for heatsensitive materials



June l2, 1962 E. w. coMlNc-:s ETAL 3,038,533

DRYING PROCESS AND APPARATUS FOR HEAT-SENSITIVE MATERIALS Filed March19, 1956 2 Sheets-Sheet 1 I lll/l10n.4

INVENTORS. fda/WM Cowzgga, Hazan/d Z )WfZa/z June 12, 1962 E. w.coM1NGSETAL 3,038,533

DRYING PROCESS AND APPARATUS FOR HEAT-SENSITIVE MATERIALS Filed March19, 1956 2 Sheets-Sheet 2 NyVENToRs.

United States 3,038,533 DRYING PROCESS AND APPARATUS FOR HEAT- SENSITIVEMATERIALS Edward W. Comings, West Lafayette, Ind., Howard A. McLain, OakRidge, Tenn., and `lohn E. Myers, West Lafayette, Ind., assignors toPurdue Research Foundation, Lafayette, Ind., a corporation of IndianaFiled Mar. 19, 1956, Ser. No. 572,575 3 Claims. (Cl. 159-4) Thisinvention relates to a method of removing materials from an aqueousmedium or vehicle and more particularly relates to a method ofseparating heat-sensitive materials in dry particulate form from anaqueous suspension or solution of the materials.

The present invention is an adaptation of the known techniques of spraydrying which render that process suitable for handling extremelyheat-sensitive materials through a complete drying period with nodeterioration of the materials. Atomization to produce a minimumparticle size is achieved with a two-fluid nozzle in which the aqueousmedium and entrained solids move through an orifice into a stream of airwhich in an area of extreme turbulence converts the medium and entrainedmaterial into minute particles. From the zone of turbulence, wheredispersion and initial volatilization of the aqueous medium haveoccurred, the dispersed particles move into a second cocurrent stream ofair where final drying, if any, is completed at a lower temperature. Theeect of the foregoing is to achieve a substanti-al drying of thedispersedparticles while minimizing the residence time of the medium inthe higher temperatures of the primary or dispersing air. The high ratioof surface to mass in the dispersion makes for high evaporation rates atan elevated temperature which would be destructive of the material, ifresidence time were of longer duration.

Further description of the invention can be had by reference to theaccompanying drawings in which:

FIGURE l is a schematic showing of a suitable arrangement of equipmentadapted to the practice of the process of this invention;

FIGURE 2 is a partial cross-sectioned view of the liquid injector forhandling the aqueous medium to be converted into a dry particulate form;

FIGURE 3 is an elevational view of the nozzle that surrounds the liquidinjector of FIGURE 2 and handles the stream of primary air employed as adispersant or atomizer of the liquid medium;

FIGURE 4 is a cross-section of the Vnozzle of FIG- URE 3 taken at line 44 in FIGURE 3; and

FIGURE 5 is a lengthwise cross-section of the housing through which asecond stream of air is introduced behind'the nozzle to serve as astabilizer for the cocurrent primary air stream and solids issuing fromthe nozzle.

By speciiic` reference to FIGURE 1, it can be seen that a blower 10,capable of delivering air at p.s.i.g. and 300 s.c.f.m., moves primaryair through valve 11 with a portion ofthe air being intermittentlyvented at Valve 12, if desired, for humidity measurements; The primaryair then passes through a heat exchanger 13 and through an electric airheater 14. Suitable pressure and temperature measuring stations arelocated at P1 and T1, respectively, with a temperature control stationbeing located at T2. Using the heat exchanger alone, primary airtemperature of 300 F. is Obtained. This temperature may be elevated tosubstantially 600-700 F. through the added eifects of heater 14. Airpassing through nozzle inlet 17 on nozzle 18 constitutes the primarydispersing or atomizing gas for the aqueous medium entering injector 19from liquid feed tank 20 through 3,038,533 Patented June l2, 1962 lter20a, metering pump 21 and rotameter 22. Shut-od? valves 23 and 24 arealso provided.

As the primary air and liquid meet and pass rapidly through the chokeorifice forming the outlet of nozzle 18, the liquid is iinely dispersedto form droplets having entrained or dissolved solids. Such droplets aredischarged from nozzle 18 into the interior of a tubular dryer 25 wherethey enter a stabilizing cocurrent stream of secondary 4air having atemperature considerably less than the temperature ofthe primary air.

Secondary air is supplied from a separate blower "26, through valve 27and a steam heater 28 capable of elevating its temperature tosubstantially 300 F. The blower 26 may be of an order capable ofdelivering air up to 1400 s.c.f.m. at substantially 2 p.s.i.g.Temperature and pressure measuring stations T3 and P2 are employed alongwith a temperature control station T4, as indicated. Secondary air isdischarged into the dryer 25 via two inlets 31 and 32 disposed onopposite sides thereof adjacent nozzle 18. The travel of the gas andentrained material is substantially unidirectional longitudinally of thedrier chamber 25, and so is the flow of secondary air which envelops it.The secondary air serves to cool the dry and dispersed particleselfectively. As a commingled body, the moist atmosphere and dried solidsmove into a tank or Vessel 33 from which separated solids are removed atthe bottom by bag-filter means, while gases and moisture are dischargedat the top through an air cleaning deep-bed filter 34. A cyclone lmayalso be used in place of this vessel.

Injector 19, as shown in FIGURE 2, comprises a feed inlet 35, coolingwater inlet 36 and cooling water outlet 37. Feed inlet 35 is connectedby tubing 38 to the discharge end of the injector, tubing 38 beingPjacketed by a concentric pipe 39 leading cool Water from inlet 3'6 to bedischarged through concentric pipe 40 returning to cooling water outlet37. The purpose of the cooling water is to preclude over heating of theliquid to be treated during the period that it is within the body of thenozzle 18 which transports the highly heated primary air foratomization. In practice, feed water conveniently obtainable at 50 to 60F. will leave the cooling jacket at temperatures on the order of F.depending on various operating conditions. While preventing over-heatingthat would destroy or cause deterioration of the entrained solids, theliquid receives enough heat as it is injected into the primary air toraise its temperature to the wet-bulb temperature of such atomizing airso that evaporation proceeds immediately.

FIGURE 3 shows nozzle 18 with the injector 19 of FIGURE 2 removed, theinjector 19 being inserted through a packing gland at the rear of thenozzle and supported by a centering ring 41 adjustable by means of anadjusting screw 41a. The centering ring is also shown in the end view,FIGURE 4. A thermocouple 42 and, pressure taps 43, 43 are illustrated inFIGURE 3 for measuring temperature and pressure. Nozzles used in thepractice of this invention are extremely sensitive to proper centeringof the injector to produce uniform low through the nozzle and avoidbuild-up of particulate material on the hot interior surfaces.

Preferably, drying chamber 25, as shown in FIGURE 5, has a uniformlysmooth inner surface which can be fabricated from sheet metal by rollingand butt welding of of 3 to 15 p.s.i.

An apparatus has been constructed to spray dry heatsensitive materialsin accordance with the aforementioned characteristics and conditions.This apparatus has been used to run the representative examples setforth below. The drying chamber 25 is of substantially uniform circularcross-section having an internal diameter of 8 inches. Axiallypositioned within the drying chamber is a nozzle 18 having an externaldiameter of about 2.5 inches and tapering, at its forward end, to anorice diameter of 0.65 inch. The drying chamber has an effective lengthof about 6 feet downstream of the nozzle orifice wherein the particlesbecome dry and the air streams commingle.

Materials to which the present technique can be applied are exemplifiedby such products as enzyme extracts, hormone extracts and beverages suchas orange juice, coffee, milk and like materials. In the successfulapplication of the described equipment to the separation of suspendedheat-sensitive biologicals, it is essential that the material be inContact with the highly heated atomizing air for an extremely shortperiod of time on the order of 0.001 to 0.01 second. Atomizing air attemperatures up to 700 F. moves past the tip of the liquid injector ataverage velocities up to 1300 ft./sec. The liquid feed lfor suchoperations is under pressures ranging from to 60 p,s.i. with thedispersing gas being under pressures It can be readily appreciated thatoperation occurs under a relatively low pressure system which finallyexhausts directly to the atmosphere so that pressures in the dryingsection are only slightly above atmospheric.

Further detailed description of the invention can be found in thefollowing representative examples dealing with the separation ofsuspensions of Serratia marcescens, a gram-negative, facultativeanaerobe and skim milk:

EXAMPLE I Cell History Organism: Serratia marcescens.

Culture medium: Tryptose broth.

Subsequent treatment: Centrifugation With culture placed in Sharplescentrifuge and cells subsequently resuspended in diluent after storageat 4 C. for 48 hours.

Feed Stock Dextrin: 20 g./l.

Ascorbic acid: 10 g./l. Total cells/ml.: 242x109. Viable cells/ml.: 5.5X 109. Percent viability: 2.3%. pH: 6.8. Total solids: 6.0%.

Inlet Dryer Conditions Feed rate: 2.48 gal/hour. Feed temp.: 69 F.

Primary air temperature at dryer inlet: 400 F.

Primary air rate: 121 cu. ft./min. (60 F., 1 atm.)..

Secondary air temperature at dryer inlet: 175 F.

Secondary air rate: 1225 to 1082 cu. ft./min. (60 F.,

1 atm).

Primary air velocity at nozzle throat: 1304 ft./sec.

Humidity of inlet air: 0.01145 lb. water/lb. air.

Outlet Dryer Conditions Air temperature: 178 F. Humidity of outlet air:0.01474 to 0.01509 lb. water/lb.

air.

Product Analysis Total cells/ml. reconstituted product: 16.5 X109.Viable cells/ml. reconstituted product: 022x109. Percent viability:1.3%.

Viable recovery: 57%.

-Viable cells/ml. reconstituted product: 013x109.

4 EXAMPLE I1 Cell History Organism: Serratiu marcescens.

Culture medium: Tryptose broth.

Subsequent treatment: Centrifugation with Sharples centrifuge andimmediate resuspension of mud in diluent.

Feed Stock Dextrin: 20 g./l.

Ascorbic acid: 10 g./ l. Total cells/ml.: 55.0 109. Viable cells/ml.0.20 109. Percent viability: 0.36%. pH: 6.7. Total solids: 4.5%.

Inlet Dryer Conditions Feed rate: 2.48 gal/hour. Feed temp.: 87 F.

Primary air temperature at dryer inlet: 400 F.

Primary air rate: 117 cu. ft./min. (60 F., 1 atm.).

Secondary air temperature at dryer inlet: 150 F.

Secondary air rate: 1234 to 1162 cu. ft./min. (60 F.,

1 atm.).

Primary air velocity at nozzle throat: 1301 ft./ sec.

Humidity of inlet air: 0.00749 lb. water/lb. air.

Outlet Dryer Conditions Air temperature: 154 F. Humidity of outlet air:0.01075 to 0.01093 lb. Water/1b.

air.

Product Analysis Total cells/ml. reconstituted product: 418x109.

Percent viability: 0.31%. Viable recovery:

EXAMPLE III Cell History Organism: Serratia marcescens.

Culture medium: Tryptose broth.

Subsequent treatment: Centrifugation with Sharples and immediateresuspension of mud in diluent.

Feed Stock Diluent- Dextrin: 20 g./l. Ascorbic acid: 10 g./l. Totalcells/ml.: 27.5X109. Viable cells/ml.: 1.40X109. Percent viability:5.1%. pH: 7.2. Total solids: 5.0%.

Inlet Dryer Conditions Outlet Dryer Conditions Air temperature: 129 F.Humidity of outlet air: 0.00961 to 0.00985 lb. Water/1b.

air.

Product Andlysis Total cells/ml. reconstituted product: 492x109. Viablecells/ml. reconstituted product: 2.50)(109. Percent viability: 5.1%.Viable recovery:

EXAMPLE IV Cell History Feed Stock Diluent- Ascorbic acid: g./l.Dextrin: g./l. Total cells/m1.: 6.6 109. pH: 7:0. Total `solid-s: 2.9%.

Inlet Dryer Conditions Feed rate: 2.49gal./hour. Feed temp.: 124 F.Primary air temperature at dryer inlet: 504 F. Primary -air rate: 114cu. ft./min. (60 F., 1 atm.). Secondary air temperature at dryer inlet:123 F. Secondary air nate: 1097 to 951 cu. L/min. (60 F.,

1 atm.). Primary air velocity at nozzle throat: 1385 ft./ sec. Humidityof inlet air: 0.00427 1b. water/lb. air.

Outlet Dryer Conditions Air temperature: 143 F. Humidity of Ioutlet air:0.00801 to 0.00840 lb. Water/lb.

air.

Product Analysis Primary air temperature at dryer inlet: 500 F.

Primary air rate: 99 cu. ft./min.. (60 F., 1 atm.).

Secondary air temperature yat dryer inlet: 125 F.

Secondary air rate: 1199 to 1095 cu. ft./mn. (60 F.,

1 atm.).

Primary air velocity at nozzle throat: 1190 ft./sec.

Humidity of inlet ai-r: 0.00985 lb. water/lb. air.

Outlet Dryer Conditions Air temperature: 131 F. Humidity of outlet air:0.01386 to 0.01421 lb. water/lb.

air.

Product Analysis Cyclone I Cyclone II Final Moisture Content, Wt.percent 3. 75 3. 8

EXAMPLE VI Feed Stock Skim milk. Total solids 9.28%.

Inlet Dryer Conditions Feed rate: 3.5 gal/hr. Feed temp.: 76 F. Primaryair temperature at dryer inlet: 502 F. P-rimary air rate: 99 cu.ft./min. (60 F., 1 atm.). Secondary air temperature at dryer inlet: 140F.

Y 6 Secondary air rate: 1140 to 1092 cu. ift/min. (60 F.,

1 atm.). Primary air velocity at nozzle throat: 1265 ft./sec. Humidityof inlet air: 0.00933 lb. Water/lb. Iair.

Outlet Dryer Conditions Air temperature: 141 F. Humidity of outlet air:0.01361 to 0.01370 lb. Water/lb.

air.

Product Andlysis Cyclone I I Cyclone II Final Moisture Content, Wt.percent 4. 52

Having thus described the invention, what is claimed is:

1. A method for producing heat-sensitive material in particulate formfrom a lliquid medium in which it is contained which comprisesprojecting a current of relatively dry secondary air at a temperaturenot in excess of 200 F. longitudinally through a tubul-ar dryingchamber, introducing a jet of said liquid medium axially into saiddrying chamber in the direc-tion of flow of said secondary air,projecting a co-current of primary air at a temperature of from about300 F. to 700 F. in `contact with said jet at an acoustic velocity up toabout 1385 feet per second, said primary air being of suiicient rate toboth break up the jet :and disperse it into line `droplets and tosimultaneously add to said droplets the heat of vaporization of theliquid, said droplets being evaporated to dryness in said tubular dryingchamber to form particles of said heat sensitive material and beingcarried along in the combined primary and secondary air moving throughsaid tubular drying chamber, said secondary air stream having a flow offrom at least 8 to 15 times that of the primary air flow suilicient toprevent recirculation of dry particles to the hot primary air stream.

2. A method for producing heat sensitive material in dry particulateform from a liquid medium containing said material which comprisesprojecting a current of relatively dry secondary air at a temperaturenot substantially above 200 F. longitudinally through -a tubular dryingchamber, projecting a jet of said liquid medium initially at atemperature not substantially above 124 F. substantially axially intothe said drying chamber into -a venturi-like orifice the outlet of whichldischarges along substantially the longitudinal axis of said tubularcharnber, projecting a co-current of primary air Iat a temperature offrom about 300 F. to 700 F. through said orifice in contact with saidjet at a velocity of from about 1190 to 1385 feet per second, saidprimary air being of suflicient rate to both break up the jet into linedroplets and to impart to said droplets the necessary heat ofvaporization, said droplets being evaporated to dryness in said tubulardrying chamber 4to form particles carried along in the combined primaryand secondary air streams, said secondary air stream flowing in volumeof from at least 8 to 15 times the volume of the heated primary air toprevent recirculation of dry particles to the hot primary air stream andat no time becoming heated substantially above 200 F.

3. A spray drying apparatus adapted for drying of heat-sensitivematerials at very high temperatures and velocities, said apparatuscomprising: an elongated cylindrical drying chamber having an inlet endand an outlet end; a nozzle assembly axially aligned with said chamberand projecting a short distance Within the inlet end thereof, saidnozzle assembly terminating in an orifice within said chamber andadapted to project a stream of a rst gas substantially axially therein;a liquid injector spaced axially within said nozzle assembly so as toinject a stream of liquid containing the heat-sensitive material towardsaid orifice within an lannular stream Iof said first gas whereby saidliquid stream Will be broken up into '2? line droplets and mixed withsaid irst gas as the latter passes beyond said orice into said chamberat velocities up to about 1385 feet per second, said liquid injectorhaving a cooling jacket about substantially its full length including aninlet and outlet for recirculating a nid coolant; an annular passageway`about said nozzle assembly extending from said inlet end of saidcylindrical chamber to project `a second gas axially of said chamberco-current with and enveloping said primary gas kand liquid streams asthe latter pass from said orifice, said annular passageway being definedby the Wall of said chamber Iand said nozzle assembly therein; -a rstgas impelling means connected to deliver a flow rate of said first gasto said nozzle assembly; a second gas impelling means connected to`deliver a much larger flow rate of said second gas to said annularpassageway, said ow rate of said second gas being from 8 to 15 times theflow rate of said first gas at normal atmospheric conditions; a rst heatexchanger connected in series with said first impelling means 'and saidnozzle assembly for controllably heating the rst gas to within a rangeof 300 to 700 F.; a second heat exchanger connected in series with saidsecond impelling means and said `annular passageway for controllablyheating the second gas up to about 300 F.; a source of liquid containingthe heat sensitive material connected to said liquid injector; and meansto control the rate of ow of said liquid to said injector.

References Cited in the le of this patent UNITED STATES PATENTS 954,451Merrell Apr. 12, 1910 1,071,692 Brigham Sept. 2, 1913 1,163,339 HaussDec. 7, 1915 1,183,098 Merrell et al. May 16, 1916 1,594,064 MacLachlanJuly 27, 1926 1,594,065 MacLachlan July 27, 1926 1,634,640 Zizinia July5, 1927 1,779,516 Stevenson et al. Oct. 28, 1930 1,830,174 Peebles Nov.3, 1931 1,866,768 Harris Iuly l2, 1932 1,964,858 Peebles July 3, 19342,297,726 Stephanoff Oct. 6, 1942 2,413,420 Stephanol Dec. 31, 19462,460,546 Stephanoff Feb. 1, 1949 2,572,321 Deanesly Oct. 23, 19512,880,794 Marshall Apr. 7, 1959

